A motor-assisted vehicle may combine power supplied by a person through the operation of levers, pedals, oars, or other movable parts of a power transmission apparatus with power supplied from an electric motor to propel the vehicle. Examples of motor-assisted vehicles include bicycles, tricycles, pedal cars, boats, aircraft, and other conveyances driven in part by an electric motor and in part by human muscle power. A motor controller in the vehicle may set operating parameters for the motor in response to a performance objective set by a person operating the vehicle. For example, a person pedaling a motor-assisted bicycle may direct the motor controller to maintain a constant forward velocity, perhaps a minimum forward velocity over hilly roads or against a headwind, a constant amount of applied pedaling power provided by the person, or another performance objective of the person's choosing. The motor controller may measure an amount of power provided by the person, calculate an amount of power to be provided by the electric motor to combine with power from the person for meeting the performance objective, and set an operating parameter for the motor to produce the calculated amount of motor power.
Power provided by a person to a vehicle in motion may be estimated from a measurement of torque exerted by the person on a movable part of the vehicle, for example bicycle pedals, or on a hand-bike, hand grips connected to rotating crank arms. The measured torque value may be combined with other measurements, for example cadence, to calculate a value of power provided to the vehicle by the person. Cadence refers to a number of revolutions of the crank arms per unit time. The motor controller may compare the value of power provided by the person with an estimate of power needed to meet the performance objective to determine how much power is to be provided by the electric motor. A setpoint value for an operating parameter for the motor may be selected to deliver the calculated amount of motor power. The motor controller may attempt to hold the operating parameter to the setpoint value in response to changes in a measured parameter related to the performance objective.
A motor controller attempting to hold a motor operating parameter to a constant setpoint value may over-react or under-react to a change in a measured value related to a performance objective. The motor controller may maintain a same setpoint value for motor operation even when environmental conditions affecting a vehicle change. For example, a motor controller may act to maintain a constant vehicle speed over a steep hill or against a sudden wind. A detected change in vehicle speed may cause the motor controller to supply more electric power to the electric motor, increasing current drawn from a battery coupled to the motor controller and possibly reducing an operating range for the vehicle.
Attempting to maintain a constant value for a setpoint related to a performance objective may lead to an unsafe operating condition. For example, when traveling on a smooth road at a set speed, if the vehicle then transitions to a rough road, the motor controller may attempt keep the vehicle speed at its fixed, smooth-road setpoint value of speed, even when the setpoint value may be unsafe for the rough road condition.
A delay in reacting to a change in a measured value related to a performance condition may cause other problems. For example, a delay in adapting electric power delivered to the electric motor, for example a delay in modifying motor power to compensate for measured torque on the crank arms, or failure of the motor control system to adapt to changing road conditions such as surface roughness, road surface slope, or changes in wind conditions, may cause a person pedaling a motor-assisted vehicle to apply uncomfortable or unsustainable amounts of power to the pedals, cause undesirable variations in vehicle speed, pedaling cadence, deplete the battery powering the motor before a desired destination is achieved, or cause other unwanted performance or safety effects.
Motor-assisted vehicles, for example motor-assisted bicycles and the like, may use a torque sensor on a crank arm or frame member of the vehicle to measure forces applied by a person riding the vehicle. For example, a torque sensor may employ a strain gauge to measure a deflection of the structure to which the sensor is attached. The deflection can be related to a force applied by the person, and the force related to a value of applied power by multiplying the force by cadence and possibly other factors. Torque sensors and strain gauges require complicated and expensive manufacturing and calibration procedures. Furthermore, torque sensors and strain gauges may be susceptible to changes in accuracy caused by temperature changes, repeated stress and wear on the sensor and associated mechanical components, damage to the sensor and associated wiring by impact or corrosion, exposure to chemicals, exposure to solar and thermal radiation, and other factors.